Magnetic frequency-controlled mode-switchable flexible microrobot enabling adaptive locomotion in biological channels for targeted drug delivery

Magnetic microrobots hold immense potential for various biomedical applications, including targeted drug delivery. However, their operational efficacy in complex, heterogeneous biological environments (e.g., vasculature with varying lumen diameters) is often constrained. To address this limitation, this study presents a magnetically driven soft microrobot capable of dual-mode locomotion, where seamless switching between oscillatory and helical motions is achieved solely by switching the external magnetic field frequency via frequency modulation. The proposed microrobot, with a millimeter-scale architecture featuring a programmed magnetization profile, exhibits C-shaped oscillation at low frequencies for rapid propulsion and terrain adaptation, and transforms into a helical rotation at high frequencies for stable navigation within confined channels. Experiments were conducted in a glycerol–water mixture to reveal that oscillatory and helical motion modes each operate within distinct, non-overlapping frequency bands. The microrobot successfully performed navigation through mode switching in both a biomimetic vascular model and ex vivo porcine organs. Furthermore, by integrating a photothermal-responsive methacrylated gelatin (GelMA) drug carrier, we demonstrated successful targeted drug delivery at a designated site triggered by near-infrared irradiation after magnetically guided delivery in a dynamic flow environment.